1. Field of the Invention
The present invention relates to a droplet ejection head, and more particularly to technology for improving fluid cross-talk and refilling characteristics of the droplet ejection head.
2. Description of the Related Art
A recording apparatus based on an inkjet method has an inkjet head in which a plurality of nozzles are arranged, and forms an image on a recording medium by ejecting and depositing inks onto the recording medium respectively from the nozzles of the inkjet head. Inkjet recording apparatuses are used widely, due to their excellent quietness, low running costs, and their capacity to record images of high quality onto recording media of various types.
An inkjet head using pressure generating elements is known. The inkjet head has a common flow channel in which ink is stored, individual supply channels connected to the common flow channel, pressure chambers connected to the respective individual supply channels, pressure generating elements which respectively cause deformation of the pressure chambers, and nozzles connected to the respective pressure chambers. In the inkjet head, the ink is supplied to the pressure chambers from the common flow channel in which the ink is stored, the pressure generating elements are driven to apply pressure to the ink inside the pressure chambers, and the ink is thereby ejected from the nozzles connected to the pressure chambers.
In an inkjet head of this kind, a phenomenon known as fluid cross-talk is liable to occur in which pressure variation in a pressure chamber affects adjacent nozzles (and especially, the meniscuses therein) through the flow channels. In order to resolve this problem, a structure is widely used in which dampers are arranged inside the flow channels, thereby impeding transmission of pressure variation to adjacent nozzles. However, in recent years, it has become difficult to arrange dampers due to the demand for higher density of the ejection elements in the inkjet head. Furthermore, when the flow channels are restricted in order to suppress the transmission of pressure variation, it is important to achieve a balance between the effects of fluid cross-talk and individual refilling characteristics.
Japanese Patent Application Publication No. 2002-321361 discloses a circulation type head having an ink reservoir on either end side of a partition defining a flow channel, wherein a total of the surface areas of opening sections of ink supply apertures and a total of the surface areas of opening sections of ink recovery apertures have prescribed relationships with a total of the surface areas of the cross sections of the flow channels taken in planes perpendicular to their lengthwise directions. By means of this composition, it is possible to prevent aggregation of ink.
However, it is not possible to control fluid cross-talk and individual refilling by simply setting a prescribed relationship between the surface area of the opening sections and the cross-sectional area of the flow channels. Fluid cross-talk and individual refilling effects are governed significantly by the flow channel resistance, and in considering the flow channel resistance, it is necessary to take account not only of the cross-sectional area of the flow channels, but also the length of the flow channels and the viscosity of the liquid.
Japanese Patent Application Publication No. 01-166963 discloses an inkjet print head having a first ink channel through which ink is supplied and a second ink channel through which air bubbles are expelled, wherein the flow channel resistance of the second ink channel is set to a range of one to two times the flow channel resistance of the first ink channel. By means of this composition, the air bubble expulsion mechanism of the inkjet print head is improved.
However, the second ink channel is not connected to a circulation channel but to a dummy nozzle provided in order to expel air bubbles, and although the second ink channel has an effect in suppressing cross-talk, the flow channel resistance ratio is designed with air bubble expulsion characteristics in mind, and fluid cross-talk and individual refilling are not taken into account.
Japanese Patent Application Publication No. 2009-056766 discloses a droplet ejection apparatus in which two or more circulation channels are arranged symmetrically about the nozzle axis. By means of this composition, symmetry is also imparted to the ink flow generated inside the connection channels, and ejection defects are prevented.
When ejecting ink, ink flow is also generated in the supply channels, as well as the circulation channels. Hence, even if the circulation channels are symmetrically arranged, it is not possible to prevent ejection defects by imparting symmetry to the ink flow produced inside the connection channels.